High Resolution Study of Low Lying Correlation Satellites in Xenon

Abstract

As the energy of light incident upon an atom or molecule is increased above that of the lowest ionization energy, a variety of neutral and ionic electronic states can be formed. The former include singly excited states converging onto an ion state with one hole in an inner orbital and doubly excited states converging onto an ionic (satellite) state with two electrons excited from the neutral configuration. These neutral resonances may decay to lower-lying ionic states through the process of autoionization. The ionic states include single hole and satellite ionic states formed directly in conjunction with a free electron. Probing the formation and characteristics of these ionic states is a primary aim of photoelectron spectroscopy. In traditional photoelectron spectroscopy the photon energy is scanned, and all electrons formed with a specific kinetic energy and angular distribution are detected. Threshold photoelectron spectroscopy uses static electric fields to allow the selective detection of electrons with near-zero kinetic energy formed in conjunction with a cationic state. Satellite states can be difficult to probe using this technique; in general, such states are formed at high photon energies, they produce low signal intensities and they contribute to a highly congested spectrum. Further, in order to discriminate against the formation of states through nearby autoionizing resonances that result in nonthreshold electrons, there is a need for a high degree of rejection of such electrons, and the effectiveness with which this is accomplished depends upon the electron optical properties of the analyzer, lenses, and electrode surfaces. Separation of such resonant from nonresonant contributions to the partial cross sections for each ionic state is therefore very difficult, but when achieved can significantly increase our understanding of the dominant processes present within an atom or molecule. The introduction of pulsed field ionization‐zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy in recent years [1] has largely overcome this problem and enabled a high-resolution spectroscopic probe of ionic states formed by excitation and subsequent field ionization.